Boris Johnson has said all U.K. nations have reached a "unanimous agreement" to go ahead with planned Christmas bubble rules.

The prime minister added, however, that people should "exercise a high degree of personal responsibility" if they do spend time with family over the festive period.

LONDON TO IMPOSE NEW CORONAVIRUS PREVENTION MEASURES AMID RISING INFECTIONS

It comes after a phone call between Westminster and the devolved nations, which took place amid growing pressure on the government to scrap the easing of the COVID-19 rules over Christmas.

Christmas decorations are displayed on the facade of the Annabel's private members club in Berkeley Square, Mayfair, London, Wednesday, Dec. 16, 2020. London and some of its surrounding areas have been placed under Britain's highest level of coronavirus restrictions beginning at 00:01 local time on Wednesday as infections rise rapidly in the capital. Under Tier 3 restrictions, the toughest level in England's three-tier system, people can't socialize indoors, and bars, pubs and restaurants must close except for takeout. (AP Photo/Matt Dunham)

At Prime Minister's Questions (PMQs), Mr. Johnson said: "Although some things are unquestionably going well… we must remember that transmission takes place asymptomatically in so many cases."

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Britain's Prime Minister Boris Johnson leaves 10 Downing Street in London, Wednesday, Dec. 16, 2020, ahead of the last Prime Minister Questions session PMQs in the House of Commons, before Christmas recess. (AP Photo/Alberto Pezzali)

"We should exercise extreme caution in the way we celebrate Christmas — we can celebrate it sensibly, but we have to be extremely cautious in the way we behave."

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UK prime minister says nations reached 'unanimous agreement' to go ahead with Christmas 'bubble' rules

'We should exercise extreme caution in the way we celebrate Christmas,' he said